The present invention relates to a skid-controlled brake system comprising a pedal-operated vacuum booster including a master cylinder to which are connected by way of pressure fluid conduits, the wheel brakes. The system further comprising a hydraulic auxiliary pressure supply system including a hydraulic pump, a pressure compensation and pressure fluid reservoir. The system further comprising wheel sensors and electronic switching circuits for detecting the wheel rotating pattern and for generating electrical brake pressure control signals to control electromagnetically operable valves for skid control.
In a brake system of this type (Patent Application No. P No. 35 02 451.8) first directional valves are provided in the brake lines interconnecting the brake chambers of the master cylinder and the wheel brakes. Through the valves, the wheel brakes can be hydraulically separated from the pressure chambers. A pressure fluid connection is established, by way of second directional valves provided in the brake lines between the return and the wheel brakes. Moreover, an auxiliary pressure control valve is inserted in the pressure line leading from the pump of the auxiliary pressure means to the brake circuits. The control input of said auxiliary pressure control valve is connected to a pressure chamber of the master cylinder so that upon commencement of the skid control and upon actuation of the pump, respectively, an auxiliary pressure proportional to the pedal force can develop. Finally, a special differential pressure detector is provided detecting the side of which the pressure is higher as a result of a defective condition, hence, indicating the type of error therefrom.
It is, therefore, an object of the present invention to substantially simplify a brake system of the type under consideration and, in particular, to reduce the number of its valves without affecting operation of the brake system.